our liberty and economic power has dwindled progressively with each passing election

That’s as much a consequence of legalisms - Bush v Gore invalidating votes in swing states, Tom DeLay kicking off a big wave of legislative gerrymandering, candidates party-flipping starting in the White Flight of the 80s/90s (WV’s governor flipped the day after the '17 election), the banning of earmarks in legislatures and the legalizing of unlimited campaign donations following Citizens United - as voting patterns.

So much power has been consolidated within the hands of party leadership and so much money has flown to affiliated party-loyal business interests that voting no longer shapes political behaviors. When Republicans can’t win an HISD board seat, they turn to the governor to simply take over the entire board by fiat. When someone in the Democratic Primary attempts to unseat an incumbent, the party spends tens of millions to defend them. When a third party bid emerges, they’re cut out of debates and excluded from news coverage save for the yellow journalism designed to dismiss you as a crank. (And, in fairness, there are tons of cranks in the 3rd party scene already).

I don’t think you can strictly attribute this to “not enough 3rd party bids”. We have consolidated political power in the same way we’re consolidating economic power.